1. Field of the Invention
The present invention relates to a magnetic recording/reproducing apparatus, such as used in an R-DAT (rotary head-digital audio tapedeck).
2. Background of the Invention
In a recently standardized R-DAT, about 2 hours of information (in an SP mode) can be recorded/reproduced on one reel of magnetic tape. Accordingly, it is desired that a desired program recorded on the magnetic tape can be searched in a short time as possible.
FIG. 1 is a block diagram of an apparatus proposed for satisfying the above-mentioned requirement. A rotary drum 1 is provided with a pair of rotary magnetic heads 2 (separately identified as 2A and 2B) having azimuth angles different from each other. A magnetic tape 3 taken up by a supply reel 4 and a take-up reel 5 is wound around the rotary drum 1 by about 90 degrees. Motors 6, 7 and 8 are arranged to rotate the respective reels 4 and 5 and the rotary drum 1. A reproducing signal produced when the rotary magnetic heads 2 trace the magnetic tape 1 is equalized by a reproducing equalizer amplifying circuit 9 and then applied to a relative velocity detection circuit 10. The relative velocity detection circuit 10 detects a relative velocity between the magnetic tape 3 and the respective rotary head 2, for example, by comparing a clock included in the reproduced signal with a reference clock. A drum servo circuit 11 compares an output signal of the velocity detection circuit 10 with a predetermined reference signal to control the motor 8 for rotating the rotary drum 1 in accordance with a resultant error signal. As a result, the rotary magnetic heads 2 run at a predetermined relative velocity determined in accordance with the reference signal relative to the magnetic tape 3.
A pulse generating circuit 12 is constituted by a pulse generator (PG) for producing about 1 to 2 pulses per one revolution corresponding to the rotational position of the rotary magnetic heads 2, a frequency generator (FG) for producing about 20 pulses per one revolution, and so on. A switching pulse generation circuit 13 generates a head switching pulse (HSWP) on the basis of an output of the pulse generator or from the respective outputs of the pulse generator and the frequency generator. The head switching pulse is applied to the reproducing equalizer amplifying circuit 9 to switch the two rotary magnetic heads 2 (2A and 2B) by changing a switch disposed in the front stage of the reproducing equalizer amplifying circuit 9. The output of the frequency generator (FG) is used also for a velocity servo for the rotary drum 1 in normal recording/reproducing.
On the other hand, pulse generation circuits 14 and 15 provided respectively corresponding to the reels 4 and 5 generate pulses in accordance with the rotation of the reels, the pulses being transferred to an operation circuit 16. The operation circuit 16 calculates a sum of the respective squares of the rotation periods of the reels 4 and 5, the resultant calculated value being transferred to a reel servo circuit 17. The reel servo circuit 17 compares the sum-of-the-squares values with a predetermined reference value so as to control the rotation of the motors 6 and 7 on the basis of a resultant error signal. Accordingly, the magnetic tape 3 is caused to run at a predetermined velocity determined in accordance with the reference value.
Thus, upon reception of a search command, a system controller 18 constituted by a microcomputer, etc., controls the reel servo circuit 17 so that the magnetic tape 3 is caused to run at a velocity higher than that in normal recording/reproducing. Predetermined code information such as a music number, an absolute time, etc., recorded in an inclined track on the magnetic tape are then reproduced to search a desired program.
If the apparatus is arranged such that the servo of the magnetic tape 3 in searching is carried out by the pulse generation circuits 14 and 15 provided respectively corresponding to the reels 4 and 5 as described above, the apparatus becomes complicated and large-sized. Further, there is such a disadvantage that the velocity of the magnetic tape 3 varies unless the reference value is changed in accordance with the length (total length) and the thickness of the magnetic tape 3.